Peel & stick membrane on top of ICF exterior walls?
jonscholl
| Posted in Energy Efficiency and Durability on
I am building a house with ICF walls….the lower level (3 walls in-ground) we are planning to finish using wire lathe & stucco on the exposed portion and the 1st Flr Level (all above grade) we are planning on installing 3/4″ vertical lathe and horizontal Hardiplank.
The question is should I install a peel & stick membrane on top of the EPS foam as a WRB or is the EPS foam sufficient for this purpose? If the peel & stick is recommended, can you recommend a particular make(s) to use? Thanks!
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Replies
Jonathan,
My first reaction is that the ICF manufacturer will have recommendations for these details, and that you are required to follow the manufacturer's recommendations.
I thought so to Martin but in fact they differed me to the stucco or siding manufacturer for their guidance as they (NADURA the ICF manufacturer) feel that this WRB element is part of the "wall finish system" . The tech guy I spoke to "felt" that it would not be needed behind 3/4" lath air gap assembly as drying potential would be sufficient but he wasn't offering that up as gospel. Ergo my reason for posting this question.
Jonathan,
All wire lath and stucco systems that I am familiar with include at least one, and usually two, WRBs (asphalt felt or building paper). That said, you could also use an EIFS system that applies synthetic stucco directly to EPS foam.
Neither EPS nor concrete is likely to be damaged by water. The main reason that you need a good WRB is so that you can integrate your window flashing with the WRB.
Any reason you don't want to use paper-backed lath?
Dealing with how to attach tar paper to the EPS I guess would be the biggest reason why not to use it. The EPS has 1-1/2" wide plastic flanges embedded into the ICF blocks at 8" OC but they are also 1/2" below the face of the EPS. So stapling anything is not a realistic option. Screwing things....like vertical lath strips works great. So I figure a peel & stick membrane is the easiest way to get a fully sealed WRB which window and door flashing tape can also be adhered to. Peel & stick is definitely more expensive than tar paper but once its installed there are no other issues. IMO.
Solution is simple. For an ICF wall just use synthetic stucco. Don't mess with metal lathe nonsense. ICF doesn't need the same air gap that a wood wall with stucco needs. Sadly, most installers go about installing stucco on an ICF wall like they do on a wood wall. No building paper, no peel & stick, no screws into the webbing, no tearing apart the EPS foam. Total waste of money.
Just use a synthetic stucco like StuccoMax, it's a two coat/one pass stucco that use fiberglass mesh. Easy & fast.
Thanks Peter. I'll look into that!